getData.js

/*
Example request: http://koop.com/craigslist/washingtondc/apartments/FeatureServer/0/query?where=price>20&f=geojson
Req is the express request object: https://expressjs.com/en/4x/api.html#req
  req.params = {
    host: 'washingtondc',
    id: 'apartments'
  }
 req.query = {
   where: 'price > 20',
   f: geojson
 }
*/
function getData(req, callback) {
  // pull pieces we need to form a request to Craigslist from the req.params object.
  const city = req.params.host
  const type = req.params.id
  // using the npm package `request` fetch geojson from craigslist
  request(`https://${city}.craigslist.org/jsonsearch/type/${type}`, (err, res, body) => {
    // if the http request fails stop processing and return and call back with an error
    if (err) return callback(err)
    // translate the raw response from Craigslist into GeoJSON
    const geojson = translate(res.body, type)
    // add a little bit of metadata to enrich the geojson
    // metadata is handled by the output plugin that is responding to the request. 
    // e.g. https://github.com/koopjs/koop-output-geoservices
    geojson.metadata = {
      name: `${city} ${type}`,
      description: `Craigslist ${type} listings proxied by https://github.com/dmfenton/koop-provider-craigslist`
    }
    // hand the geojson back to Koop
    callback(null, geojson)
  })
}